Hydroxy-terminated copolymers of butadiene and ferrocene derivatives

ABSTRACT

The copolymers of vinyl ferrocene (VF) and butadiene are disclosed along with preparative procedures therefor. The copolymers are produced in an organic solvent when polymerization is initiated by an azo type initiator selected from the initiators consisting of azo-bis-(2-methyl-hydroxyvaleronitrile), azo-bis-(hydroxyethyl-2-methyl proprionate), and azo-bis-(2-methyl-3-hydroxy proprionitrile). The copolymers serve as a binder for solid propellant compositions and also serve to increase the burning rate of solid propellants wherein used.

United States ?atent 1 Baldwin et a1.

[ 1 Feb. 27, 1973 1 HYDROXY-TERMINATED COPOLYMERS OF BUTADIENE AND FERROCENE DERIVATIVES [75] Inventors: Mart G. Baldwin, Newtown, Pa.; Samuel F. Reed, Jr., Huntsville, Ala.

[73] Assignee: The United States of America as represented by the Secretary of the Army [22] Filed: Nov. 25, 1969 [21] Appl. No.: 886,601

[52] US. Cl ..260/82.1, 149/19 [51] Int. Cl. ..C08d 1/34, C08d 3/06 [58] Field of Search ..l49/l9, 109; 260l82.1, 83.1

[56] References Cited UNITED STATES PATENTS 6/1969 Sayles ..149/19 1/1971 Mofiettetal ..149/109X OTHER PUBLICATIONS Levi, Ferrocene Polymers, Picatinny Arsenal, Dover, N.J., 1966, pp. 1, 2,12 and 13.

Primary ExaminerLeland A. Sebastian AttorneyI-larry M. Saragovitz, Edward J. Kelly, Herbert Berl and James T. Deaton [57] ABSTRACT 2 Claims, No Drawings HYDROXY-TERMINATED COPOLYMERS OF BUTADIENE AND FERROCENE DERIVATIVES BACKGROUND OF THE INVENTION Considerable literature exist on the preparation of polybutadiene with hydroxy-terminal groups prepared by both anionic and free radical initiators.

The preparation of vinyl ferrocene may be accomplished by the method disclosed by F. S. Arimoto and A. C. Haven, J. Chem. Soc., 77, 6295 (1955).

The prior art indicates that the burning rates of solid propellants compositions can be increased by introduction of certain iron-containing additives. N-Butyl ferrocene, a ferrocene derivative, is an iron containing compound which has been employed as an additive to increase the burning rate of solid propellants. Many ferrocene derivatives have been utilized as additives for this purpose, usually in the form of liquids which also serve as plasticizing agents. In the liquid state the ferrocenes display the inherent disadvantages characteristic of any liquid additives, such as loss by evaporation, migration, etc., and consequently, the propellant systems suffer, particularly on long term storage.

Thus, a need exists for a modified form of ferrocene additive which form is not subject to being lost by evaporation or migration from a stored propellant composition.

An object of this invention is to combine the ferrocene additive with the binder being utilized in the propellant system.

Another object is to provide a ferrocene derivative and a binder material via a polymerization technique to combine into a serviceable prepolymer suitable for propellant mixing and curing.

A specific object of this invention us to provide a liquid copolymer which is capable of undergoing a cure reaction when used in a propellant composition to form a rubber-like binder material having a burning rate catalyst agent as an integral part thereof.

SUMMARY OF THE INVENTION Vinyl ferrocene is copolymerized with butadiene in an inert organic solvent after the polymerization reaction is initiated by a suitable initiator such as one selected from the initiators consisting of azo-bis-(2- methyl-5-hydroxy-valeronitrile), azo-bis-(2-methyl-3- hydroxy-propionitrile), and azo-bis-(hydroxyethyl-2- methyl propionate). The liquid copolymer is characterized by its molecular weight which is in the range of from about 1000 to about 10,000, its hydroxy-end group content from about 0.1 weight percent to about 2.5 weight percent, and its iron content from about 0.24 weight percent to about weight percent. The liquid copolymer is capable of undergoing a cure reaction to a final rubber-like state.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The copolymer formed by reaction of butadiene with vinyl ferrocene is useful as a binder and also as a burning rate catalyst for solid propellant compositions.

The liquid copolymer is characterized by its preferred molecular weight range from about 1000 to about 10,000, its preferred hydroxy-end group content from about 0.1 weight percent to about 2.5 weight percent, and its preferred iron content from about 0.24 weight percent up to about 10 weight percent. The liquid copolymer of butadiene and vinyl ferrocene is produced by a procedure as described by the descriptive technique set forth below as Example I. Table I below sets forth the experimental data on preparation of butadiene-VF copolymers. Table II below, sets forth the physical property data for butadiene-VF copolymers produced with concentrations set forth in Table l.

The Butadiene-VF mole ratios may vary from approximately 100:1 to about 1:1. The organic solvents wherein copolymerizations are conducted may be toluene or dioxane. Polymerization temperatures may conveniently be maintained in the range of 60-80C. Reaction times may vary over the range of 24-120 hours; however, a reaction time in the range of about 72 hours is preferred.

Copolymers having molecular weights ranging from about 1,000 to about 10,000 hydroxy-end group contents from about 0.1 to about 2.5 weight percent of the copolymer and an iron content up to about 10 weight percent of the copolymer are easily obtained by varying the reaction conditions and concentrations of reactants and initiators.

EXAMPLE] PROCEDURE FOR POLYMERIZATION OF BUTADIENE AND VINYL FERROCENE To a glass high-pressure reactor (Aerosol tube) are introduced 30 ml. of toluene, 0.43 g (0.002 moles) VF, and 1.53 g (0.00606 moles) azo-bis-(Z-methyl-S- hydroxy-valeronitrile), (AMHV). The reactor is attached to a vacuum line and deaerated by three alternate freeze-thaw cycles. At this point 10.8 g (0.2 moles) of butadiene are condensed into the reactor, and the reactor is removed from the vacuum line and placed in an oil bath at 66-67C. Heating is continued for a period of 72 hours. After cooling, the reactor is vented, the solvent removed by evaporation and the copolymer reprecipitated by dissolving in ether followed by the addition of methanol. After decanting the solvents, the copolymer is stripped of excess solvents on a rotatory evaporator and finally dried at 7075C. under reduced pressure (1 millimeter) for a period of 24 hours. The yield of copolymer is 4.1 g. (35.6 percent). Evaporation of the decanted solvents gives an additional 2.0 g. of the copolymer containing the low molecular weight copolymer and impurities. This material is not characterized further. The liquid copolymer (methanol insolubles) is characterized by its molecular weight (4100), hydroxy-end group content (1.34 weight percent) and elemental analysis (percent P e-0.24).

TABLE I.EXPERIMENTAL DATA ON TREPARA'IION OF BUTADIENE-VF COPOLYMERS T0mp.: 66-67"; Time: 72 hours Mole Weight ratio AMlIV Solvent m mly- Ylul l No. Butadiene (B) VF lllV1- (mole) (.90 ml.) lll 'J (1.5.) [lfll' f lll 0. 00001; 'lulumm 4. 1

0. 006062 Dioxmu: .1. 2 Mi. 0

Table 11. Physical Property Data for Butadiene VF Copolymers Molecular Weight on Fe No. Weight Found/Calcd. Found/Calc'd. 1. 4100 1.34 /0.83 0.24 [0.99 2. 3700 12910.92 2.3 [7.43 3. 2800 1.42 /1.06 0.58 /0.99 4 3200 1.32 /1.2. 2.9 /7.43

Calculated H weight made on the basis of two OH groups per chain for the molecular weight values reported.

*' Calculated Fe Content made on the basis of the ratio of comonomers initially charged into the reactors.

The copolymers of this invention may be used as the binder-catalyst for a solid propellant composition. The copolymer may be used in the propellant composition in an amount from about 5 weight percent to about 30 weight percent. The remaining propellant ingredients exclusive of processing aids (such as lecithin) and trace amount of additives may be comprised of a plasticizer such as isodecyl pelargonate, a metal fuel such as aluminum, and an inorganic oxidizer such as ammonium perchlorate.

An example of a propellant composition using the copolymers of this invention is set forth under Example 11 below.

EXAMPLE II Ingredient Weight Percent Butadiene/Vinyl Ferrocene Copolymer binder lsodecyl pelargonate plastieizer Aluminum powder Ammonium perchlorate The burning rate for the propellant formulation of Example II compared with a standard containing only polybutadiene is higher by about 20 percent. The

propellant formulation of Example 11 does not require an additional burning rate catalyst, and the formulation may be varied to incorporate a higher binder content and a higher iron content. The burning rate of the propellant increases as the iron content increases. The iron content may also be controlled by the amount of vinyl ferrocene copolymerized with butadiene as well as the amount of copolymer selected for use in the formulations. Those skilled in the art will recognize that the other propellant ingredients may be varied to include metal additives (e.g., aluminum powder or other powdered metals used in the art) in amounts from about 5 to about 20 weight percent, inorganic oxidizer such as, ammonium perchlorate from about 10 to about 72 weight percent. Other plasticizers may be used with the copolymers of this invention. Among the important plasticizers are nonvolatile organic liquids or low melting solids, especially the phthalic adipate and sebacate esters, and aryl phosphate esters. Plasticizer content is determined by the desirable properties required for a propellant formulation. Generally, plasticizer amount from about 5 to about 30 weight percent is the range meeting most requirements. Special processing aids such as lecithin and trace amount of additives known in the art for their specific contributions to the ballistic, castibility, and storage properties of the propellant may be added to the propellant formulation.

We claim:

1. A method for preparing hydroxy terminatedcopolymers of butadiene and vinyl ferrocene comprising reacting vinyl ferrocene and a suitable polymerization initiator in an inert organic solvent with butadiene at a reaction temperature and for a reaction time period. sufficient for said reaction to take place after which solvent removal is effected and said copolymers are dried at a suitable drying temperature while under reduced pressure; said initiator being selected from azo-bis-( 2-methyl-5 -hydroxy-valeronitrile), azo-bis-( 2- methyl-3-hydroxy-propionitrile), and azo-bis-(hydroxyethyl-2-methy1 propionate); said inert organic solvent being selected from dioxane and toluene; said reaction temperature being in the range of about 60C to about 80C; said reaction time being from about 24 hours to about 120 hours; said drying is accomplished at a suitable temperature in the range of about C to about C and said reduced pressure is in the range of about 1 millimeter.

2. The copolymers prepared by the method of claim 1 from said reacting butadiene and vinyl ferrocene in mole ratios from approximately :1 to 1:1, said copolymers being characterized by a molecular weight in the range from about 1,000 to about 10,000, hydroxy-end group content of about 0.1 weight percent to about 2.5 weight percent, and an iron content of about 0.24 weight percent to about 10 weight percent. 

2. The copolymers prepared by the method of claim 1 from said reacting butadiene and vinyl ferrocene in mole ratios from approximately 100:1 to 1:1, said copolymers being characterized by a molecular weight in the range from about 1,000 to about 10, 000, hydroxy-end group content of about 0.1 weight percent to about 2.5 weight percent, and an iron content of about 0.24 weight percent to about 10 weight percent. 